Silencer and exhaust gas system comprising a silencer

ABSTRACT

A silencer is provided that is intended to be connected to a gas flow with pressure fluctuations, such as for example downstream a combustion engine, the silencer comprising a housing provided with an envelope surface and two side surfaces and an inlet opening and an outlet opening arranged in the envelope surface.

TECHNICAL FIELD

[0001] The invention refers to a silencer according to the preamble of claim 1 and an exhaust gas system according to claim 15.

STATE OF THE ART

[0002] Silencers are generally used to reduce emissions of sound from gas flows with pressure fluctuations. The emissions of sound are reduced according to known silencer technique in that resonance phenomenon In resonance chambers damps the oscillation modes of the gas within given frequency interval, by introducing turbulent flow paths which break laminar flow with pulsations and result in that the energy contained in the gas flow is spread from said oscillation modes to a wider energy spectrum. The sound is also reduced through that the silencer induces a fall of pressure of the gas flow. This fall of pressure give rise to energy losses and in case the silencer is used at a unit producing energy, the degree of efficiency of the unit decreases. In case the silencer is used at a combustion engine, the decrease in efficiency give rise to a larger environmental effect In the form of exhausts of carbon dioxide for the same amount of useful energy produced.

[0003] During design of silencers, the silencer's ability to reduce the acoustic pressure must be weighed against the fall of pressure that the silencer give rise to and thereby the amount of energy that the silencer consumes.

BRIEF DESCRIPTION OF THE INVENTION

[0004] An object of the invention is to provide a silencer with a low counter pressure and a good ability of silencing noise, which silencer is cheap to manufacture. This object is attained by a silencer according to the characterizing portion of claim 1. A flow of sounds through a channel can be seen as a series of increases of pressure with intermediate decreases of pressure that passes after each other through the channel. By forming the partition wall as a band which is folded to Z shape to a package which forms a set of inlet channels on one side of the partition wall and a set of outlet channels on the other side of the partition wall, an opposite directed flow is formed on opposite sides of the partition wall.

[0005] As a result, increases of pressure and decreases of pressure will pass each other at regular intervals in time and space. As the wall through its folded design is made partly non-rigid, differences in pressure will be balanced whereby silencing of noise is achieved. Thus, each time a pressure impulse passes a shock wave, the amplitude of both will be decreased.

[0006] In a preferred embodiment the silencing effect can be further increased by damping the the movement of the partition wall with friction. Further, the partition wall can be provided with perforations whereby pressure pulsations through the perforations can give rise to increased ability of silencing noise.

[0007] In a specially preferred embodiment the partition wall is provided between the inlet opening and the outlet opening in such a way that it extends between turning chambers arranged in connection with the side walls of the silencer, and is provided with a set of inlet channels which leads from the inlet opening to said turning chamber and a set of outlet channels which leads from from said turning chamber to the outlet opening, whereby the partition wall divides the flow in two opposite directed flow paths from the inlet opening via turning chambers and which flow paths meet at the outlet opening. This design give rise to a silencer where the opposite directed flow paths give rise to a very good noise reducing effect. Besides, each of the flow paths is characterized in that the flow moves in a forward and backward path with opposite directed flow on each side of the partition wall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be further described in connection with enclosed drawings, in which

[0009]FIG. 1 shows a manufacturing process for a silencer according to the invention,

[0010]FIG. 2 shows the silencer in detail, with an indication of the flow paths through the silencer, and

[0011]FIG. 3 shows, in detail, surfaces of the partition wall according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0012]FIG. 1 shows the manufacturing of a silencer according to the invention. A partition wall 1 b comprised in the silencer is formed from a metal band 1 a being formed by pressing, rolling or the like. The metal band is further formed in a pressing step between rollers where the metal band 1 a on one hand is given a surface structure 20, which is shown in an enlarged view in FIG. 1, and on the other hand a set of alternately directed folding notches 2, 3. Thus, the partition wall is formed from a band which is folded to Z shape to a package which forms a set of inlet channels on one side of the partition wall and a set of outlet channels on the other side of the partition wall.

[0013] The surface structure of the metal band comprises a set of protrusions which are provided to, when the metal band is folded and comprises a set of inlet channels and outlet channels, give rise to an increased turbulence during flow through the channels in the partition wall, whereby additional flow ways are formed according to what will be explained in the following. In a preferred embodiment of the invention the protrusions are made as a corrugation obliquely made on the band, preferably inclined 40°-70° in relation to the direction of the folding notches 2, 3. The protrusions also functions as spacers and give rise to a rigid construction even when the band is made in thin material such as sheet metal with a thickness less than 0,2 mm, preferably less than 0,1 mm. Even material with a thickness down to and less than 0,05 mm can be used with a good result.

[0014] In a second manufacturing step the metal band 1 a is folded to a partition wall 1 b which is provided with a set of inlet channels 21, whereby one is shown is unfolded position in FIG. 2 and a set of outlet channels 22. Further, the partition wall 1 b is provided with seals 5, 6 in the respective end portions of the metal band 1 a, which seals are intended to bear on an upper and a lower surface 22, 23 of a housing 4 surrounding the partition wall 1 b. Each of the inlet channels 21 are formed by an upper and a lower substantially plane surface 24, 25 and a fold 26 which connects the upper and the lower surface. In the same way each of the outlet channels 22 are formed by an upper and a lower substantially plane surface 27, 28 and a fold 29 connecting the upper and the lower surface.

[0015] Each of said sets of inlet channels and outlet channels are thus defined by an upper and a lower substantially plane surface and a fold connecting said surfaces, and where the upper and the lower substantially plane surfaces are made substantially parallel.

[0016] The corrugations at adjacent folds in the folded metal band cross each other and form a stable and non-rattling package with large volume when the metal band is pressed together. Between the folds of the band flow channels are made with a stable geometry. It is advantageous for the silencing effect if each of these channels with help of the corrugations form a large amount of irregular flow ways of different length. Thus, the sound waves that pass through the channels are divided into many dephased wave parts that tend to quench each other. By forming crossed corrugations the number of sound paths and sound reflection points are made large. Preferably, the band is made so that direct flow is prevented and so that it is not possible to look through it.

[0017] Further, according to an embodiment of the invention, the partition wall can be provided with perforations whereby pressure pulsations through the partition wall give rise to additional silencing of noise.

[0018] Normally, the partition wall divides the flow into two substantially opposite directed flow paths from the inlet opening via turning chambers and which flow paths meet at the outlet opening. The expression substantially opposite directed flow paths means that the average flow through the paths are opposite directed whereby the use of protrusions, for example in the form of corrugations for generating a large amount of flow ways within the respective opposite directed flow path, does not change the fact that the flow paths are substantially opposite directed.

[0019] In a preferred embodiment of the invention the partition wall 1 b is formed with such a geometry that each of the inlet and outlet channels in said sets of inlet and outlet channels 21, 22 has an extension length from turning chamber 7 to turning chamber 8, which substantially exceeds the extension length from an inner fold edge 26 to an outer fold edge 29 of said inlet and outlet channels.

[0020] In a third manufacturing step the partition wall 1 b is placed in said housing 4 whereafter the housing is closed by mounting the upper surface 22 to it.

[0021] The housing 4 is provided with an envelope surface 30 and two side surfaces 31, 32. Together the envelope surface and the side surfaces form a closed volume. Two opposite surfaces of the envelope surface are provided with an inlet opening 9 and an outlet opening 10. The positioning of the partition wall 1 b inside the housing is made such that the folds 29 of the outlet channels are placed against the surface of the envelope surface that is provided with said inlet opening and the folds 26 of the inlet channels are placed against that side of the envelope surface 30 that is provided with said outlet opening 10. In a preferred embodiment of the invention the partition wall 1 b and the housing are formed with a rectangular cross section, which leads to an effective manufacturing process. Two turning chambers 7, 8 are provided in connection with said side surfaces 31, 32. The turning chambers provides flowing from the inlet channels 21 to the outlet channels 22.

[0022] To attain an effective silencing of noise the partition wall is formed with at least 10 pairs of inlet channels and outlet channels. Further, in a preferred embodiment, the partition wall is formed so that the relation between the extension length from turning chamber to turning chamber and the extension length from an inner fold edge where the band is folded counterclockwise to an outer fold edge where the band is folded clockwise is between 1,1 and 6, preferably between 1,4 and 3. Further, the channels have Such a design that the extension length from the folds 26 of the inlet channel 21 that face the side of the housing 4 where the outlet opening 10 is arranged, to the folds 29 of the outlet channel 22 that face the side of the housing 4 where the inlet opening 9 is arranged substantially exceeds the height from an upper channel wall to a lower channel wall. In a preferred embodiment the relation between the height from an upper channel wall to a lower channel wall and the extension length from an Inner fold to fold between {fraction (1/30)} and {fraction (1/100)}.

[0023] In FIG. 3 is shown In detail the design of the partition wall with the above mentioned surface structure in the form of a corrugation obliquely made on the band, preferably Inclined 40° -70° in relation to the direction of the folding notches 2, 3.

[0024] According to a preferred embodiment of the Invention the Inlet opening and the outlet opening are symmetrically placed In respect of the partition wall whereby the flow path from inlet opening to outlet opening Is the same independent of through which turning chamber the flow passes. In an additional preferred embodiment the inlet opening and the outlet opening are positioned directly opposite each other on opposite sides of the housing.

[0025]FIG. 4 schematically shows an exhaust gas system for a combustion engine. The combustion engine is provided with a inlet 35 and an Intake and exhaust manifold 36 which is connected to said exhaust gas system. A first catalyst 37 is arranged downstream the outlets of the combustion engine 33. A silencer according to the above described invention Is mounted downstream this catalyst.

[0026] The Invention should not be limited to the above described embodiments, but can be varied within the scope of the enclosed claims, for example the partition wall can be made in another manufacturing process and the cross section of the partition wall can have a cross section other than rectangular. 

1. Silencer intended to be connected to a gas flow with pressure fluctuations such as for example downstream a combustion engine, the silencer comprising a housing (4) provided with an inlet opening (9) and an outlet opening (10), a partition wall (1 b) and a turning chamber (7, 8) where the flow is carried from one side of the partition wall (1 b) to the other whereby the partition wall (1 b) divides the flow in two substantially opposite directed flow paths on both sides of the partition wall (1 b), characterized in that the partition wall (1 b) is formed from a band (1 a) which is folded to Z shape to a package which forms a set of inlet channels (21) on one side of the partition wall (1 b) and a set of outlet channels (22) on the other side of the partition wall (1 b).
 2. Silencer according to claim 1, characterized in that the partition wall (1 b) is non-rigidly formed, whereby pressure fluctuations on both sides of the partition wall are reduced.
 3. Silencer according to claim 2, characterized in that the thickness of the partition wall (1 b) is less than 0,2 mm, preferably less than 0,1 mm.
 4. Silencer according to any of claims 1-3, characterized in that each of the sets of inlet channels (21) and outlet channels (22) comprises an upper and a lower substantially plane surface (24-25, 27-28) and that the substantially plane surfaces (24-25, 27-28) are formed with a set of protrusions which are provided to generate a large number of irregular flow ways through each of the substantially opposite directed flow paths.
 5. Silencer according to claim 4, characterized in that the protrusions have such an extension length from the upper and lower plane surfaces (24-25, 27-28) comprised in the channels (21, 22) that it is not possible to look from one end to the opposite end of the channels (21, 22).
 6. Silencer according to any of claims 1-5, characterized in that each of the sets of inlet channels (21) and outlet channels (22) is defined by an upper and a lower substantially plane surface (24-25, 27-28) and a fold (26, 29) connecting the surfaces and that the upper and the lower substantially plane surfaces (24-25, 27-28) are substantially parallel.
 7. Silencer according to any of the preceding claims, characterized in that the partition wall (1 b) forms at least 10 inlet and outlet channels (21, 22) positioned on top of each other.
 8. Silencer according to any of the preceeding claims, where the package is provided with a set of inner fold edges (26) where the band is folded counterclockwise and a set of outer fold edges (29) where the band is folded clockwise, characterized in that the extension length from an inner fold edge (26) to an outer fold edge (29) of the inlet and outlet channels (21, 22) substantially exceeds the height from an upper channel wall to a lower channel wall.
 9. Silencer according to claim 8, characterized in that the relation between the height from an upper channel wall to a lower channel wall and the extension length from an inner fold edge (26) and an outer fold edge (29) is between {fraction (1/30)} and {fraction (1/100)}.
 10. Silencer according to any of the preceeding claims, the silencer comprises a housing (4) provided with an envelope surface (30) and two side surfaces (31, 32), where the inlet opening (9) and the outlet opening (10) are arranged in the envelope surface (30), characterized in that first a and a second turning chamber (7, 8) are arranged in connection with the side surfaces (31, 32), and that the partition wall (1 b) extends between the respective turning chamber (7, 8), whereby the set of inlet channels (21) leads from the inlet opening (9) to the turning chamber and the set of outlet channels (22) leads from the turning chamber to the outlet opening (10), whereby the partition wall (1 b) divides the flow in two substantially opposite directed flow paths from the inlet opening (9) via turning chambers and which flow paths meet at the outlet opening (10).
 11. Silencer according to claim 10, characterized in that the relation between the extension length from turning chamber (7) to turning chamber (8) and the extension length from an inner fold edge (26) to an outer fold edge (27) is between 1,1 and 6, preferably between 1,4 and
 3. 12. Silencer according to any of claims 10 or 11, characterized in that the inlet opening (9) and the outlet opening (10) are symmetrically positioned with respect to the partition wall (1 b), whereby the flow path from the inlet opening (9) to the outlet opening (10) is the same independent of through which turning chamber (7, 8) the flow passes.
 13. Silencer according to claim 12, characterized in that the inlet opening (9) and the outlet opening (10) are positioned midway between the edge regions of the partition wall (1 b) that are connected to the turning chamber (7, 8).
 14. Silencer according to any of the preceeding claims, characterized in that the partition wall (1 b) is provided with perforations.
 15. Use of a silencer according to any of the preceeding claims in a exhaust gas system for a combustion engine downstream a first catalyst. 